In recent years, a ferro-electric memory (FeRAM: Ferro-electric Random Access Memory) is being developed in which information is held in a ferro-electric capacitor structure by using polarization inversion of a ferro-electric. The ferro-electric memory is a nonvolatile memory in which held information is not lost even when a power supply is off, and attracts attention in particular since realization of a high integration degree, a high-speed drive, a high durability, and a low power consumption can be expected.
Recently, there is an increasing request for a low voltage operation of a ferro-electric memory. In order to achieve the low voltage operation, it is necessary to thin a ferro-electric film being a capacitor film of a ferro-electric capacitor.
However, there is a problem that thinning of the ferro-electric film leads to a decrease of a polarization inversion amount and an increase of a leak current.
As a cause of the decrease of the polarization inversion amount, it can be thought that due to thinning of the ferro-electric film lattice matching of an interface between the ferro-electric film and an upper electrode affects an electric property. If the lattice matching is not good, a high polarization inversion amount cannot be obtained.
Further, it can be thought that a cause of the increase of the leak current similarly depends on a state of the interface between the ferro-electric film and the upper electrode. When the ferro-electric film is crystallized by a heat treatment, a grain boundary is formed on that interface, and on that occasion a space occurrs in the grain boundary. If a material of the upper electrode is filled into this space portion, an effective film thickness of the ferro-electric film becomes thin, leading to the increase of the leak current.
Japanese Laid-open Patent Publication No. 2000-260954 and Japanese Laid-open Patent Publication No. 2000-252444 disclose configurations in which a composition of Pb, Zr, Ti of a capacitor film made of PZT is adjusted by using an SrRuO3 (SRO) film for a part or an entire of an upper electrode. However, in such a case, a leak current increases compared with a case in which an SRO film is not used.